The present invention relates, in general, to control systems for regulating the environment within animal growth houses, and in particular to the control of humidity and temperature within poultry houses for economic optimization of broiler chicken production.
The production of broilers in the poultry industry involves a "grow out" stage in which many thousands of young chicks are delivered to a poultry house, where they are sheltered and provided with food and water through a growth cycle of about six to eight weeks. At present, about 5 billion birds are produced per year. The chicks are not individually caged, but are massed in the poultry house by the thousands. A typical poultry house is a steel-truss or wood frame structure with seven foot high walls, a width of 40 to 50 feet, and a length of 300 to 600 feet. One or two curtain dividers, or partitions, are usually provided along the length of the house to divide the building into sections to restrict the access of the birds since very young chicks do not require the entire floor space. In addition, the building may be provided with large openings along its length for natural ventilation, the opening being provided with curtains to control air inflow and to maintain heat in the winter. Alternatively, the building may be totally enclosed, and dependent on mechanical ventilation for substantially all air exchange, in which case fans may be located at spaced positions along the length of the house. A plurality of heaters are normally provided for maintaining the temperature at a desired level. The heaters may be spaced along the length of one wall, preferably the wall opposite the fan location. Cooling is not usually provided.
One section of the house is used as a brooder portion, and incorporates either large brooder stoves within the house or external heaters. Both are capable of maintaining a relatively high temperature in the brooder section. An automatic feed system supplies specified quantities of feed to the birds, and an automatic watering system provides a regulated quantity of water to the poultry house.
For the first three weeks of life, chicks are not able to control their own body temperature, and thus are very susceptible to changes in temperature within the poultry house. For this reason, the brooder stoves or heaters in the brooding section are capable of maintaining the temperature level constantly high, in the range of 85.degree.-95.degree. F. When the chicks are small, most of the poultry house can be closed off by the partitions, so that only a small area, for example 25% of the total area, need be maintained at this high temperature. However, after about 20 or 21 days, the chicks begin to be able to regulate their own body temperature, and the brooder section does not have to be maintained at this high level. In many systems, the brooder stoves are simply turned off at this time, and the temperature level within the house is maintained by the body heat of the birds themselves. Occasionally, supplemental heat must be added during cooler weather, and during warmer weather the houses must be well ventilated to prevent overheating, for chickens are susceptible to temperatures that are too high. After about the 21st day one or both of the divider partitions may be removed to allow access to the entire building. The period prior to this time is usually referred to as the brooding period; the following time is usually referred to as the growout period.
In a poultry house, the entire floor normally is covered with a "litter" material, usually wood shavings, which remains in place for about a year before it is changed. During that time, the litter accumulates a great deal of fecal matter, water, spilled feed, and the like, so that its nature and consistency gradually changes over that period of time. The condition of the litter directly affects the quality of the air in the poultry house, and to a large extent determines the air quality. Accordingly, bird health and performance are directly related to the moisture level of the litter in the house.
Chickens are extremely sensitive to dust, and if the litter becomes too dry, respiratory problems such as bird air saculitis can affect an entire flock. On the other hand, if the litter remains too moist, it encourages the growth of harmful bacteria, incubating diseases such as coccidiosis which is one of the most devastating of the poultry diseases, and which can infect an entire flock. The danger of such infection requires that medication (coccidiostats) be added to the feed, in present poultry houses, and this medication is very expensive. Thus, it is critical for the health of the flock, and for the economic operation of the poultry house, to maintain the moisture level in the litter at a healthful level.
Since there is a continuous air flow through poultry houses, the relative humidity level in the air is changeable, and depends to a large extent on the temperatures inside and outside the house, but also depends on the moisture level in the litter. An important factor in determining the moisture level in the litter is the relative humidity of the air, for the litter acts as a sponge to absorb moisture from the air or to give moisture up to the air, depending on their relative moisture conditions. Although short-term variations in the air relative humidity may be produced by controlling the air flow through the house, the long-term moisture level in the poultry house litter changes relatively slowly, so that changes in ventilation rates do not immediately result in corresponding changes in litter condition. Instead, litter changes occur over a several hour period.
Another factor affecting air quality in a poultry house is the amount of ammonia produced by the litter. This varies with the condition of the litter, and other factors, but must be taken into account when controlling ventilation rates, for if the ammonia level is too high, ventilation must be increased, even if it is at the expense of desired humidity and temperature levels.
In prior control systems for poultry houses, it was recognized that the humidity level and the air temperature were important for maintaining the health of a flock. However, the prior art did not fully comprehend the nature of the interaction between the heating system, the humidity levels, and the operation of the ventilating system and thus did not attempt to control them in such a way as to maintain optimum conditions wherein the health of the poultry is safeguarded, while at the same time, holding the energy and other costs required to maintain the desired environmental conditions to a minimum. For example, attempts to control the temperature within a poultry house can adversely affect the control of humidity, for the addition of heat to raise the air temperature increases the moisture capacity of the air and tends to dry out the litter. Similarly, increasing temperatures in warm weather or unacceptably high ammonia levels can result in the operation of ventilating fans, increasing the air flow and thereby drying out the litter. Thus, the requirements for heating or ventilation may conflict with the humidity level requirements within the poultry house. These conflicting requirements make environmental control very complex, and have precluded the effective control of litter moisture on a continuous basis. Further, prior systems have not provided a mechanism for obtaining environmental control in such a way as to provide a maximum economic return from the poultry house.
The operation of various heaters and ventilators in poultry houses was, in the past, controlled manually by an operator who made periodic measurements or subjective assessments of litter moisture level and interior temperature levels, with the operator being required to then experiment with the heating and ventilation controls in an attempt to regulate the air quality on the basis of those measurements or assessments. Since the relationships are complex, and since the operator would only make periodic measurements and adjustments, such manual systems led to wide, and often harmful, fluctuations in temperature and humidity, and presented an almost insurmountable problem even to experienced operators, particularly during periods of extremely variable weather, as often occurs in the spring and the fall. This difficulty was compounded by the fact that accurate measurements of litter moisture are extremely difficult to make, not only because the condition of the litter can vary widely over the length and width of a poultry house, but because the measurements provided by a limited number of available sensors will only provide an indication of surface condition for a very small area, rather than the actual condition of the litter as a whole. Thus, the use of such sensors would often cause the operator to make control determinations on the basis of inaccurate or incomplete data, thereby causing incorrect operation of ventilating fans or heaters. In addition, such sensors have the further disadvantage of being quite costly.
More recently, attempts have been made to provide computerized control of the poultry house environment, and extremely complex control systems have been developed which attempt to take into account all of the large number of variable conditions. However, in reality such computerized systems essentially replicate the manual control of a poultry house environment, and for this reason have not been satisfactory. A common feature of all such prior control systems is that they operate on the basis of preselected criteria, such as charts which provide specified values of air temperature and relative humidity, and operate to those preselected values only. Such systems cannot take into account the dynamic changes that occur within a poultry house from day to day and are even less able to take into account changes from hour to hour. These dynamic changes include changes in litter type, variations in litter conditions from the time of bird placement, changes in the birds themselves both as to size and as to health, changes in feeding patterns in response to air temperature, and changes in factors such as outside air temperature and humidity. These prior art systems do not provide for qualitative, continuing assessments of existing inside and outside conditions, but simply operate in accordance with preselected values.
It is essential that a poultry house be operated for maximum economic return. The two principal factors in an economical operation are: (1) the cost of maintaining the poultry house environment and the associated bird performance, including the rate of growth and feed consumption, all of which are extremely temperature dependent; and (2) bird health. Optimal environmental control must be directed to both aspects. Systems which operate to preselected conditions of air temperature and humidity cannot operate economically at all times, but instead depend upon whether the preselected values happen to be best for the particular poultry house at the particular time, under the particular weather and animal conditions. Sometimes the preselected values are correct; most of the time they are wrong. Various studies have shown that optimal economic conditions are dynamic and are house specific, and cannot be specified by a fixed general management method. Yet the existing systems are so complex, in attempting to incorporate all of the various factors involved in environmental control, that an operator can do little to correct the situation or compensate for errors which produce an uneconomic operation.